Prop Proto Board supply under-voltage question

Searider

If I supply a regulated 5v to the properller proto board, will the first stage regulator just pass the 5v on to the second stage and the 5v rail?
In other words, what is the behavior of the first regulator when the supply voltage is below it's drop-out threshold ?

thanks

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Searider

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kwinn

No, the output voltage will be less than the input voltage. A linear regulator needs the input voltage to be higher than the regulated output voltage to work properly. The voltage difference depends on whether it is a standard or LDO regulator. See "http://power.elecdesign.com/tutorial/index.cfm?action=Tutorial&tutorialID=14" for a description.

Mike Green

You'll lose some voltage to the regulator, probably on the order of the drop-out threshold which is around 1V.

Leon

If you really want to supply the board from 5V you could disconnect the 5V regulator and feed the 5V input direct to the 3.3V regulator input. I only use a 3.3V supply on the Propeller boards I design for my own applications.

Leon

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Amateur radio callsign: G1HSM

Searider

Thanks Mike and Leon. I concidered feeding the 5v after the regulator but it would be nice to keep the power receptical in-circuit. I guess it is not to be though. I need 12v and and also to power the Proto board. I don't want to build a regulator and cant find any dual output 12v & 9v regulators available. I guess I will just bypass the first stage regulator. I'll look at the Board, I may be able to just clip the regulator off and short the input and output pins with a jumper. That way I can still use the Power connector.

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Searider

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Leon

That should work. It would be quite easy to restore the board to its original condition if you wish.

Leon

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Amateur radio callsign: G1HSM